Mannich bases from isolated amine adducts

ABSTRACT

Mannich bases as curing agents for epoxy resins, characterized in that to prepare the Mannich base an isolated amine adduct is used obtainable by reacting a) an amine containing at least three active amine hydrogens with b) an epoxide compound containing on average one or more than one epoxide group in the molecule, optionally using a solvent, there being an excess of a) relative to reactive groups of components a) and b), and subsequently the adduct formed is isolated from free amines. Curable epoxy resin compositions comprising these Mannich bases are suitable owing to good obtainable surface properties in particular for coating, adhesively bonding and enhancing metallic and mineral substrates, as adhesive and sealant, and for producing mouldings and sheetlike structures.

The present Invention relates to Mannich bases prepared using isolatedamine adducts obtainable by reacting amines with epoxide compounds andthen isolating the adducts from free amines; in particular, in onepreferred embodiment, the preparation of Mannich bases by transaminatingthe aforementioned isolated amine adducts with Mannich bases; and to theuse of these Mannich bases as curing agents for epoxy resins.

Curable compositions based on amine compounds and epoxy resins have longbeen used in industry for coating and enhancing metallic and mineralsurfaces, and also as adhesives and sealants. The cure rate of suchsystems is too low for many applications, particularly when coating isto be carried out at low temperatures, e.g. in winter. Numerousexperiments have been performed aimed at achieving sufficientlow-temperature curing through the addition of external accelerators.Use has been made, for example, of tertiary amines and phenols, withpreference being given to tertiary amines such astrisdimethylaminomethylphenol, for example. However, since theseexternal accelerators do not participate in the curing reaction, theyare subsequently present in free form in the cured thermoset and can bewashed out later on. Moreover, free phenols in particular aretoxicologically objectionable. For this reason it is common to usereaction products of phenols, aldehydes and amine compounds as curativesor accelerators. The thermosets cured with epoxide compounds, however,generally have poor surface qualities. Thus, greasy films, formation ofhydrates and development of texture are frequent occurrences, meaningthat such Mannich bases can often not be used in the surface sector. Thesubsequent formation of adducts of the abovementioned compounds,although possibly contributing to improving the level of properties, isunable to eliminate these surface defects completely. The fraction offree residual amines results, moreover, in the abovementioned compoundshaving a strong odour nuisance effect and in some cases beingtoxicologically objectionable.

It was an object of the present invention, therefore, to provide curingagents which have a sufficient cure rate at low temperatures incombination with as long a pot life as possible and, at the same time,satisfactory surface qualities such as, for example, a low propensity toform texture or greasy films. This object is achieved in accordance withthe invention through the use of specially prepared Mannich bases basedon isolated amine adducts as curatives for epoxy resins. These Mannichbases are obtainable by reacting an amine with aldehydes and phenols,characterized in that first of all, before the amine is reacted with thealdehyde and the phenol component, in a first step an adduct is formedfrom the amine with a preferably monofunctional compound, and thisadduct is then isolated. This isolated adduct, in a second step, isreacted conventionally to form a Mannich base or, alternatively, is usedfor the transamination of a Mannich base starting compound.

Surprisingly, the use of these specially prepared Mannich bases ascuring agents for epoxy resins leads to surface properties in the curedproducts which, comparatively, are much better than when using Mannichbases with a comparable degree of adduct formation but prepared not fromamine adducts isolated to start with but rather from subsequent adductsof Mannich bases.

The isolated amine adducts are prepared using epoxide compounds,preferably monofunctional glycidyl ethers, such as phenyl glycidylether, cresyl glycidyl ether, glycidyl ethers based on distilled cashewnut shell oil, glycidyl ethers based on monoalcohols, styrene oxide,etc.

Amine compounds used are those amines which contain at least 3 activehydrogen atoms in the molecule. Preferred amines are polyalkylenamines,especially polyethylenepolyamines such as, for example,aminoethylpiperazine, ethylenediamine, diethylenetriamine,triethylenetetramine and tetraethylenepentamine.

To prepare the isolated amine adducts the epoxide compound is added to a1.5 to 8 molar, preferably 2 to 3 molar, excess of the amine componentat from 60° C. to 80° C. with stirring and, after reaction has takenplace, the excess of amine compound is separated off by distillation,where appropriate under reduced pressure, to give a product isolatedfrom free amines.

The isolated adducts, in particular those with monofunctional epoxidecompounds, are liquid at room temperature.

As a phenol component for preparing the Mannich bases it is possible,for example, to use the following: monophenols, such as phenol, cresol,the isomeric xylenols, para-tert-butylphenol, nonylphenol, naphthols andalso diphenols and polyphenols such as resorcinol, hydroquinone,bisphenol A, bispenol F or novolaks.

As an aldehyde component it is preferred to use trioxane, formaldehydeor paraformaldehyde.

The Mannich bases are prepared from the isolated amine compounds bymethods known per se, by introducing the isolated amine adduct compoundwith the phenol component, where appropriate in the presence of diluentsand/or solvents, and adding the aldehyde component in portions atelevated temperature, dissolving it, and, after heating up to 160° C.,separating off the water of reaction. Examples of diluents and/orsolvents which can be used include the following: xylene, toluene,alcohols, ethers, water. The nature of the diluents/solvents used isdependent on the dissolution capacity of the reactants. Thus, dependingon the isolated adducts or phenols employed, the solubility may bebetter in one or another solvent. Good results are essentially obtainedusing xylene as solvent.

This invention firstly provides, therefore, Mannich bases characterizedin that to prepare the Mannich bases an isolated amine adduct is usedobtainable by reacting a) an amine containing at least three activeamine hydrogens with b) an epoxide compound containing on average one ormore than one epoxide group in the molecule, optionally using a solvent,there being an excess of a) relative to reactive groups of components a)and b), and subsequently the adduct formed is isolated from free amines.

The invention further provides Mannich bases characterized in that forthe preparation of the Mannich base from an amine, an aldehyde and aphenol derivative the amine used is an isolated amine adduct obtainableas described above.

For the preparation of the Mannich bases, in addition to the isolatedadducts, it is also possible to use as well, in part, polyamidoamideswith or without imidazoline groups, prepared from polyamine compoundsand organic acids.

One particularly preferred embodiment of the invention are Mannich basescharacterized in that for the preparation of the Mannich bases a Mannichbase obtained by reacting an amine, an aldehyde and a phenol derivativeis subjected to transamination with an isolated amine adduct of theinvention.

Mannich bases prepared by transamination are described in, for example,DE-A 28 05 853 and in EP-A 0 684 268. The advantage of these compoundsis their extremely low phenol content and hence a lower toxicity. Insuch a transamination reaction amine compounds are exchanged for aminecompounds of a Mannich base, preferably mono, bis- ortris(dimethylamino)phenol, by heating both components to more than 110°C., in the course of which the secondary amine compound present on thephenol component, generally dimethylamine, is eliminated and removedfrom the reaction mixture by distillation. Also described therein areadducts of such exchange Mannich bases with various compounds,particularly glycidyl ethers. The disadvantage of such compounds, hereagain, is the still considerable fraction of free, unreacted amine. Thesource of this free amine fraction is the linkage products which arealso formed, in accordance with the following scheme (using a diamineand dimethylaminomethylphenol by way of example):

where the dimethylamine, HN—(CH₃)₂, leaves the reaction mixture at thetemperatures customary during the transamination reaction and iscollected in a cold trap. The unreacted residues of the normallylow-volatility amine compounds used for the transamination remain in theproduct.

Free amines, however, have an intense odour and are thus a nuisanceduring processing, particularly in enclosed areas, and are frequentlytoxicologically objectionable. The aim of the invention was to eliminatethe aforementioned disadvantages here as well and to provide curingagents which cure rapidly at low temperatures (<5° C.) and have a lowfree amine content.

This object has been achieved through the curing agents of theinvention, which are characterized in that, as already described above,in a first step an isolated adduct of an amine compound with an epoxidecompound is prepared and, in a second step, this adduct is subjected toa transamination reaction with a Mannich base, the isolated amine adductadding to the phenol of the Mannich base and being exchanged for theamine, preferably a secondary amine, which is present on the phenol.

Moreover, such products, particularly whentris(dimethylaminomethyl)phenol is used, have a very low phenol content.In addition to the isolated amine adducts it is also possible to preparethe Mannich bases in part from polyaminoamide compounds prepared frompolyamines and organic acids.

The invention accordingly further provides curing agents for epoxidecompounds, obtainable from isolated amine adducts and Mannich bases bymeans of a transamination reaction.

The Mannich bases needed to prepare the compounds of the invention arepreferably Mannich bases of phenol, formaldehyde and dimethylamine,which are available commercially, for example, from the company Rohm &Haas under the name DMP. These products include DMP 10 or(dimethylaminomethyl)phenol, DMP20 or bis(dimethylaminomethyl)phenol andDMP 30 or tris(dimethylaminomethyl)phenol. Preference is given here totris(dimethylaminomethyl)phenol. Tris(dimethylaminomethyl)phenol is alsoavailable commercially from Vantico as curative HY-960-1 CH. There is noneed to make special mention of the fact that Mannich bases based onother phenols (e.g. bisphenol A or bisphenol F, cresol etc), aldehydesand amine compounds can also be used.

The degree of transamination is guided by the desired properties of thecompounds of the invention. It can be between 1% and 100%. That is,between 1% and 100% of the amino groups, preferably secondary aminogroups, that are present on the Mannich base used can be exchanged. Thismust be viewed as a function of the degree of substitution of theMannich base employed. For example, in the case of bis(dimethylaminomethyl)phenol only one amino group can be exchanged, whilein the case of bis(dimethylaminomethyl)phenol a maximum of 2 aminogroups and in the case of tris(dimethylaminomethyl) phenol a maximum of3 amino groups can be exchanged. Preferred in accordance with theinvention are compounds in which the amino groups have not beencompleted exchanged. Taking tris(dimethylaminomethyl)phenol as theexample, these are compounds containing unexchanged dimethylaminegroups.

Particular preference is given to transamination products based ontrisdimethylaminomethylphenol in which the degree of exchange is from50% to 99%, more preferably from 60% to 95%. The isolated amine adductsused to prepare the compounds of the invention have been describedabove.

The compounds of the invention obtained by transamination mayadditionally have adducts formed from them with compounds capable ofreaction with amine compounds, for the purpose of establishing specificproperties or setting the amine equivalent. For this purpose it is alsopossible in particular to use the compounds used for forming adducts ofthe amine compounds.

The invention further provides curable compositions comprising a Mannichbase of the invention, an epoxy resin, and, optionally, the auxiliariesand additives that are customary in epoxy resin chemistry.

The invention further provides for the use of the curable compositionsfor coating, adhesively bonding and enhancing metallic and mineralsubstrates, as adhesive and sealant, and also for producing mouldingsand sheetlike structures.

EXAMPLES Example 1 Preparation of an Isolated Adduct

567 g of tetraethylenepentamine TEPA (3 mol) are charged to a reactionvessel. After heating to about 60° C., 185 g of cresyl glycidyl ether (1epoxide equivalent) are added over the course of about 60 minutes. Thetemperature rises to 90° C. The reaction product is then heated to 260°C. and the excess amine is separated off under reduced pressure (<1mbar) . Distillate: 380 g (2 mol) of TEPA. Viscosity/25° C.: 1500 mPa.s(Haake rotational viscometer VT 550).

Example 2 Preparation of a Mannich Base from an Isolated Adduct

374 g (about 1 mol) of the isolated adduct from Example 1 are charged toa reaction vessel together with 31.3 g of phenol (0.33 mol) and 200 g ofxylene and the initial charge is homogenised. Then, after heating to 60°C., 30 g (1 mol) of paraformaldehyde are added in portions at not morethan 90° C., and dissolved. After heating to 150° C., the water ofreaction formed (18 g) is separated off using a water separator. Whenthe total amount of water has been separated off the xylene is separatedoff under a reduced pressure of 50 mbar. This gives a yellowish productof high viscosity.

A) 70 g of the product is dissolved in 24 g of xylene and 6 of butanol.The 70% solution has a viscosity of 3400 mPa.s.

B) 70 g of the product are dissolved in 30 g of benzyl alcohol. The 70%solution has a viscosity 13100 mPa.s.

The theoretical amine equivalent of the solutions is approximately 120.

Example 3 Transamination

561 g (about 1.5 mol) of the isolated adduct from Example 1 arehomogenised with 265 g of DMP 30 (about 1 mol) and heated at 145° C. ina distillation apparatus with distillate cooling until 67.5 g ofdistillate have been eliminated. (This corresponds to a degree oftransamination of 50%, based on all of the substitution possibilities.)Analysis by gas chromatography reveals the distillate to be puredimethylamine. The amount of distillate corresponds to 1.5 mol ofdimethylamine.

Cooling gives a yellowish product of high viscosity.

A) 70 g of the product are dissolved in 24 g of xylene and 6 g ofn-butanol. The 70% solution has a viscosity of 2000 mPa.s.

B) 70 g of the product are dissolved in 30 g of benzyl alcohol. The 70%solution has a viscosity of 8700 mPa.s.

The theoretical amine equivalent of the solutions is approximately 145.

Example 4 Transamination

748 g (about 2 mol) of the isolated adduct from Example 1 are reacted inaccordance with Example 2 with 265 g (1 mol) of DMP 30 until 90 g (2mol) of dimethylamine have been eliminated.

(Degree of transamination 66%).

A) 70 g of the product are dissolved in 24 g of xylene and 6 ofn-butanol. The 70% solution has a viscosity of 3200 mPa.s.

B) 70 g of the product are dissolved in 30 g of benzyl alcohol. The 70%solution has a viscosity of 14400 mPa.s.

The theoretical amine equivalent of the solutions is approximately 132.

Example 5 Subsequent Adduct Formation

100 g of the solution from Example 4 are heated to 70° C. and an adductis subsequently formed with 5 g of cresyl glycidyl ether (epoxideequivalent 182). The product has a viscosity of 18800 mPa.s. Thetheoretical amine equivalent is approximately 145.

Example 6 Comparative Example to Example 4, Adduct Formed Subsequentlyfrom Exchanged Mannich Base, Same Amounts Employed

378 g (2 mol) of tetraethylenepentamine are reacted in accordance withExample 2 with 265 (1 mol) of DMP 30 (tris(dimethylaminomethyl)phenol)until 90 g (2 mol) of dimethylamine have been eliminated (degree oftransamination 66%). An adduct is subsequently formed from the productusing 370 g of cresyl glycidyl ether at from 80° C. to 100° C.

A) 70 g of the product are dissolved in 24 g of xylene and 6 g ofn-butanol. 70% solution has a viscosity 3800 mPa.s.

B) 70 g of the product are dissolved in 30 g of benzyl alcohol. Theproduct has a viscosity of 16500 mPa.s.

The theoretical amine equivalent is approximately 132.

Example 7 Use Example, Surface Comparison

The solutions A) of the compounds of the invention from Examples 2 to 6are homogenised with a bisphenyl A diglycidyl ether (epoxide equivalent:185) Araldite GY 250 (Vantico AG) and a portion of the mixture isapplied to a glass plate using a 100μ spiral and stored in acontrolled-climate cabinet at 5° C. for 24 hours. An assessment is madeof the surface quality. The amounts and results are given in Table 1.TABLE 1 The surfaces are assessed on a scale from 1 to 10, where 1denotes the best and 10 the worst evaluation. Water spotting is testedby applying water to the coating. A visual evaluation is made of thewhitening of the film after 1 hour. Greasy film and sticking aredetermined by touch-testing the surface by hand, wearing a rubber glovefor protection. The formation of hydrates is likewise assessed visually.g curing a) c) Example agent per Water b) Hydrate d) Sum A) 100 gAraldite spotting, Greasy form- Stick- of a) solutions GY 250 1 h filmation ing to d) 2 65 4 3 4 5 16 3 78 3 3 3 4 13 4 71 3 3 3 4 13 5 78 2 22 3 9 6 71 6 3 6 4 19

Example 8 Use Example, Cure Rate

The solutions B) of the compounds of the invention from Examples 2 to 6are homogenised with a mixture of a bisphenol A/F diglycidyl ether witha glycidylised fatty alcohol (epoxide equivalent of 194 g) Araldite GY793 (Vantico). A portion of this mixture is poured into a sample vesselwith a thickness of 6 mm and stored in a controlled-climate chamber at5° C. A measurement is made of the cure rate to Shore D. The results areset out in Table 2. TABLE 2 Example B) g curing agent per solutions 100g Araldite GY 793 1 day 2 days 3 days 7 days 2 62 25 48 67 75 3 75 34 5674 76 4 68 30 52 69 74 5 75 37 60 76 78 6 68 29 52 70 77Discussion of the Results:

The cure rates of the products are comparable. As compared with thepreferred embodiment of the transaminated products (Examples 3 to 5) thespecimen cast with the directly prepared Mannich base (Example 6) has asomewhat lower initial hardness.

The surfaces of the products of the invention (Examples 2 to 5)surprisingly exhibit a lower level of hydrate formation and of waterspotting than comparative Example 6. This is also evident from thedirect comparison of Examples 4 and 6. This result was unforeseeable,since the reactants in these two products are present in equal amountand differ only in that, in the example according to the invention, anisolated adduct is used to prepare the Mannich base, and the comparativeexample is subsequently adducted with the same amount of glycidyl ether.A striking finding is the further significantly improved surface qualityand somewhat better cure rate of the inventive Example 5. Alsosurprising is the viscosity of the inventive Example 4, which is lowerby about 15% in direct comparison with comparative Example 6.

1-11. (canceled)
 12. A process for producing a Mannich Base comprisingthe steps of:
 1. forming an isolated amine adduct;
 2. reacting theisolated amine adduct with an aldehyde component and a phenol component.13. The process of claim 12, wherein the isolated amine adduct is formedby reacting (a) an amine compound containing at least three active aminehydrogens with (b) an epoxide compound, there being an excess of (a)relative to reactive groups of components (a) and (b), and thereafterseparating off the excess amine compound to yield an adduct isolatedfrom free amines.
 14. The process of claim 13, wherein the epoxidecompound is a monofunctional glycidyl ether.
 15. The process of claim13, wherein the amine compound is a polyalkylenamine.
 16. The process ofclaim 15, wherein the amine compound is a polyethylenepolyamine.
 17. Theprocess of claim 13, wherein the epoxide compound is added to a 1.5 to 8molar excess of the amine component.
 18. The process of claim 17,wherein the epoxide compound is added to a 2 to 3 molar excess of theamine component.
 19. A process for producing a Mannich base comprisingthe steps of:
 1. forming an isolated amine adduct;
 2. subject theisolated amine adduct to a transamination reaction with a Mannich base.20. The process of claim 19, wherein the isolated amine adduct is formedby reacting (a) an amine compound containing at least three active aminehydrogens with (b) an epoxide compound, there being an excess of (a)relative to reactive groups of components (a) and (b), and thereafterseparating off the excess amine compound to yield an adduct isolatedfrom free amines.
 21. The process of claim 20, wherein the epoxidecompound is a monofunctional glycidyl ether.
 22. The process of claim20, wherein the amine compound is a polyalkylenamine.
 23. The process ofclaim 22, wherein the amine compound is a polyethylenepolyamine.
 24. Theprocess of claim 20, wherein the epoxide compound is added to a 1.5 to 8molar excess of the amine component.
 25. The process of claim 24,wherein the epoxide compound is added to a 2 to 3 molar excess of theamine component.
 26. The process of claim 19, wherein the isolated amineadduct is subjected to a transamination reaction with a Mannich base ofphenol, formaldehyde and dimethylamine.
 27. The process of claim 26,wherein the Mannich base is tris(dimethylaminomethyl)phenol.
 28. Theprocess of claim 19, wherein the transamination reaction has a degree ofexchange from 50% to 99%.
 29. The process of claim 28, wherein thetransamination reaction has degree of exchange from 60% to 95%.
 30. Theprocess of claim 28 or claim 29 wherein the Mannich base istrisdimethylaminomethylphenol.
 31. A curable composition comprising: (a)a Mannich based produced by the process according to claim 1 or claim19; and (b) an epoxy resin.